Alkylene glycols, in particular monoalkylene glycols, are of established commercial interest. For example, monoalkylene glycols are used in anti-freeze compositions, as solvents and as base materials in the production of polyalkylene terephthalates e.g. for fibres or bottles.
The production of alkylene glycols by liquid phase hydrolysis of alkylene oxide is known. The hydrolysis is generally performed by adding a large excess of water, e.g. 20 to 25 moles of water per mole of alkylene oxide. The reaction is considered to be a nucleophilic substitution reaction, whereby opening of the alkylene oxide ring occurs, water acting as the nucleophile. Because the primarily formed monoalkylene glycol also acts as a nucleophile, as a rule a mixture of monoalkylene glycol, dialkylene glycol and higher alkylene glycols is formed. In order to increase the selectivity to monoalkylene glycol, it is necessary to suppress the secondary reaction between the primary product and the alkylene oxide, which competes with the hydrolysis of the alkylene oxide.
One effective means for suppressing the secondary reaction is to increase the relative amount of water present in the reaction mixture. Although this measure improves the selectivity towards the production of the monoalkylene glycol, it creates a problem in that large amounts of water have to be removed for recovering the product.
Considerable efforts have been made to find an alternative means for increasing the reaction selectivity without having to use a large excess of water. The hydrolysis of alkylene oxides to alkylene glycols can be performed with a smaller excess of water in a catalytic system. Therefore, these efforts have usually focused on the selection of more active hydrolysis catalysts and various catalysts have been disclosed in the literature.
Catalytic processes, promoting a higher selectivity to monoalkylene glycol product at reduced water levels are known (e.g. EP-A-0,156,449, U.S. Pat. Nos. 4,982,021, 5,488,184, 6,153,801 and 6,124,508). Such catalysts often comprise a strongly basic (anionic) exchange resin, often with quaternary ammonium or quaternary phosphonium electropositive complexing sites, coordinated with one or more anions (e.g. metalate, halogen, bicarbonate, bisulfite or carboxylate).
Further examples of catalytic processes known for the reaction of alkylene oxides to alkylene glycols are given in JP 2001151713 and JP 2001151711, wherein a catalytic composition comprising a halide ion and a bicarbonate ion is used to convert an alkylene oxide to the corresponding alkylene glycol in the presence of carbon dioxide and water.
JP-A-56,092,228 is directed to the use of molybdenum and/or tungsten as a catalyst for the conversion of alkylene oxide to alkylene glycol, again in the presence of carbon dioxide and water.
U.S. Pat. No. 4,307,256 describes the reaction of alkylene oxides with water and carbon dioxide in the presence of a tertiary amine catalyst for the production of alkylene glycols. In U.S. Pat. No. 4,160,116 a similar system is described, wherein the catalyst used is a quaternary phosphonium salt.
EP-A-1,034,158 is directed to the use of a catalytic composition comprising a macrocyclic chelating compound complexed with an ionic compound selected from the group comprising halogenides, carboxylates, hydrogen carbonates, hydrogen sulphites, hydrogen phosphates and metalates, for the hydrolysis of alkylene oxides to alkylene glycols.
In addition, processes for the production of alkylene glycols from alkylene oxides, comprising a two-step process, have been described in the art. Such processes involve the reaction of alkylene oxides with carbon dioxide in the presence of a catalyst, followed by subsequent thermal or catalytic hydrolysis of the resultant alkylene carbonate. Examples of such two-step processes include those described in JP-A-57,106,631 and JP-A-59,013,741.
Catalysts suitable for the hydrolysis of alkylene carbonates are described in U.S. Pat. No. 4,283,580, which is directed to the use of molybdenum or tungsten in metal or compound form as catalysts in the production of substituted or unsubstituted ethylene glycols by the reaction of substituted or unsubstituted ethylene carbonates with water.
Although progress has been made in the hydrolysis of alkylene oxide to alkylene glycol, the need for new processes with increased levels of conversion using highly active and selective catalyst compositions still remains.